The use of monomeric epoxy-functional silanes in coating, adhesive, sealant and composite applications is known. Recently, oligomeric epoxy-functional silanes were disclosed as an important component of waterborne coatings. For example, U.S. Pat. Nos. 7,732,552 and 7,893,183 disclose water-based coating compositions containing oligomeric epoxy-functional silanes and one or more optional ingredients such as surfactants, pH adjusting agents, co-solvents, monomeric silanes, binders, crosslinkers and pigment paste dispersions. These oligomeric epoxy-functional silanes are prepared from glycidoxy silane and/or cycloaliphatic epoxy silane having 2 or 3 alkoxy groups and less than 1.5 equivalents of water in the presence of a catalyst, wherein the water is continuously fed during the reaction.
Oligomeric epoxy-functional silanes can also be prepared by other methods. For example, U.S. Patent Application Publication No. 2010/0191001 discloses oligomeric epoxy-functional silanes prepared by using 0.001 to less than 5 mol of water per mole of alkoxy function of silanes and not using any further hydrolysis or condensation catalyst apart from boric acid as a hydrolysis catalyst and condensation component.
Unfortunately, although the use of oligomeric epoxy-functional silanes in the coating compositions may improve the chemical resistance of the coatings, the flexibility of the coatings may be compromised due to the higher degree of cross-linking associated with the use of high molecular weight oligomeric epoxy-functional silanes. Further, the volatile organic compound (VOCs) emissions in the form of alcohols from coatings containing the low molecular weight epoxy-functional silane oligomers disclosed in the prior art may be high due to partial hydrolysis of the monomeric epoxy-functional alkoxysilane.
Accordingly, there is a continuing need in the coatings industry for a stable, zero or low VOC containing epoxy-containing polysiloxane oligomer composition that improves the chemical resistance of the coatings while at the same time, maintains or improves the flexibility of the coating containing this epoxy-containing polysiloxane oligomer composition. The present invention provides an answer to that need.